Over time, forwarding rates for routers have increased rapidly, whereas control plane processing capabilities have increased at a slower rate. A ratio between forwarding plane speeds and control plane speeds is very large (e.g., a factor of one-thousand or greater) and has been increasing over time. Existing methods for Internet protocol (IP) multicast are relatively control-plane intensive. One approach, known as a bit index explicit replication (BIER) forwarding method, has been introduced into the Internet Engineering Task Force (IETF) to allow many multicast groups to be simultaneously supported with minimal state in a core of a network. In the BIER forwarding method, only an ingress router for any particular packet flow needs to know which egress routers need to receive any particular packet. The BIER forwarding method does not require any explicit tree-building protocol, nor does the BIER forwarding method require intermediate routers to maintain any per-flow state. A router that implements the BIER forwarding method is known as a bit-forwarding router (BFR).
In the BIER forwarding method, a multicast packet includes a bit string that indicates end or destination BFRs to receive the multicast packet, and each end BFR includes a unique identifier (ID) that maps to a bit of the bit string. Each next hop BFR analyzes the bit string and replicates the multicast packet to neighboring BFRs that are on a shortest path to the end BFRs indicated by the bits in the bit string.